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Fakultät für Chemie und Pharmazie - Digitale Hochschulschriften der LMU - Teil 04/06 Podcast
Loss of the SNARE protein Sec22p selectively represses caesium accumulation in yeast and plants

Loss of the SNARE protein Sec22p selectively represses caesium accumulation in yeast and plants

Fakultät für Chemie und Pharmazie - Digitale Hochschulschriften der LMU - Teil 04/06 vor 13 Jahren

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The rare alkali ion caesium (Cs+) is assimilated by eukaryotes,
even though it is not an essential nutrient. It poses an
environmental concern through the anthropogenic release of its
radioisotopes, 134Cs and 137Cs. Bioavailability and long half-lives
favour its uptake and accumulation in plants, via which
radiocaesium can be introduced to the food chain. Cs+ ions are
taken up via potassium-(K+)-related pathways due to the biophysical
similarity of these cations. This makes it difficult to solely
manipulate Cs+ accumulation in plants without disturbing the
homeostasis of essential ions at the same time. This work shows
that the soluble N-ethylmaleimide sensitive factor attachment
receptor (SNARE) Sec22p, previously described as a member of the
protein sorting machinery, specifically affects Cs+ accumulation in
yeast by regulating the selectivity of vacuolar deposition. A
similar phenotype became apparent for a homologous plant protein,
SEC22. The loss of Saccharomyces cerevisiae Sec22p reduces Cs+
uptake by more than half, while at the same time leaving essential
cations undisturbed. Mathematical modelling of wild-type and mutant
Cs+ uptake kinetics proposes that sec22Δ is defective in vacuolar
compartmentalisation of Cs+, which is proven by biochemical
fractionation. Morphological alterations were not produced by the
loss of Sec22p, only a Cs+-dependent vacuolar fragmentation can be
observed. These results indicate a so far undescribed function of
Sec22p in assuring a non-selective ion deposition to the vacuole,
which is necessary in ion detoxification, while its loss induces
discrimination against vacuolar Cs+ deposition. A developmentally
controlled loss-of-function mutant of the orthologous gene SEC22
(At1g11890) in A. thaliana displays a similar phenotype, having
specifically reduced Cs+ enrichment without detrimental growth
defects, thereby translating the yeast findings to a multicellular
context. Furthermore, a functional complementation of the yeast
mutant Cs+ phenotype by the plant gene transcript was possible.
Selective reduction of Cs+ accumulation in plants by loss of a
single gene product represents a new route to limit radiocaesium
input to the food chain without disturbing basic plant nutrition
and growth.